1. Field of the Invention
In general, this invention pertains to convertible fixed wing aircraft of the type that can be flown as a more-or-less conventional fixed wing aircraft, or be rapidly and automatically converted to an automotive street vehicle in order to arrive at one's final destination quickly and conveniently without having to transfer to a ground vehicle at the airport.
More particularly, the means to arrive at rapid conversion from aircraft mode to automobile mode involves, quite simply, rotation of the wing from a transverse orientation with respect to the fuselage or body to a longitudinal orientation whereby the vehicle's width is less than the maximum legal width of eight feet (2.44 m), without requiring any dissembly of any part including wing, tail or fuselage that may be potentially inconvenient and time-consuming. Conversion from automobile mode to aircraft mode (and vice-versa) may be done nearly instantaneously while the vehicle is traveling at legal highway speed, thereby allowing new three-dimensional use of the current highway system in the 21st century (at designated segments only) with the concept of "vertical exit" and "vertical merging" (or take-off and landing in today's language).
2. Discussion of the Prior Art
The idea of a single vehicle that can function as an aircraft to cover long distances in the shortest time, and then as a highway vehicle that can be driven from the airport to the ultimate destination, is an attractive one. However, there are many problems that make this ideal concept difficult to realize, and while many have attempted to design such a vehicle, there has never been a successful product that has reached the market.
The problem has been in integrating the functions and structural requirements of the two vastly different vehicles into a single, user-friendly construction that requires a minimum of human intervention in switching from the automotive to the aircraft configuration. The technological bases for both invidual systems are highly developed, and it is necessary that this high level of technology for both systems be incorporated in a single system while maintaining the performance of these different systems.
The structural design requirements for an aircraft are quite different from those of an automobile, particularly in the matter of weight and aerodynamic resistance, which must be held to the minimum level, whereas in an automobile, weight and aerodynamic streamliness are not nearly as important consideration. The aerodynamic drag of an automobile body is many times that of an airplane fuselage, due in part to the unstreamlined underbody, with all of the exposed power transmission and suspension gear. Instead, in the automobile, ground handling and comfort especially smoothness and quietness are much more highly stressed, whereas in the light aircraft, ground handling is particularly poor especially in windy condition, and that the cockpit noise and vibration level in these aircrafts are quite objectionable to the non-enthusiasts.
The overall length of the automobile is made as short as possible in order to facilitate parking and maneuverability, whereas the aircraft's fuselage is much longer in order to provide adequate pitch damping and control authority necessary to be certified for production under FAA regulation part 23.
For an air-ground convertible vehicle that is reasonably operable in both modes, a great deal of compromise must be made among above factors, such that the final product up to now has been inefficient and has inferior flying characteristic in comparison to a production aircraft, at the same time requiring considerable amount of assembly or dissembly of wings, fuselage and tail section during the conversion.
The case in point is the well publicized effort of a major aircraft company Consolidated Vultee in 1947 in which an automobile body is attached to a wing-engine-tail assembly for flying and to be completely detached from this assembly for ground travel mode. Due to the aerodynamically inefficient automobile body as well as excessive weight because the automobile portion contains its own engine and transmission for ground travel, the final Convair Model 118 ConvAirCar of 1947 flew poorly with cruise speed of only 125 mph (200 km/h) and after a non-fatal crash in November 1947, the program was cancelled.
After the obvious inconvenience of the ConvAirCar in which the wing and tail must be left behind at the airport in its roadable mode, another highly publicized project, that of Mr. Molt Taylor's Aerocar I, improved on the ConvAirCar due to its ability to trailer its own wings, tails and the tail half of the fuselage. The Aerocar is only one of two roadable aircraft designs ever certified by the FAA for limited production status. Mass production of the Aerocar was almost begun by Ling-Temco-Vought company of Dallas, Tex., but was cancelled due to insufficient pre-production orders. Considerable efforts of at least two persons is required in order to assemble the wings, fuselage and tail prior to flight, and that this conversion can only be carried out in calm to light wind only. One of the owner of one of four Aerocar I prototype ever produced, Mr. Ed Sweeney stated that he is not keen on trailering the wings and tails, that he does not want to do it very often and that he has spent sometimes 45 minutes in converting the Aerocar from its street-legal mode to its flight-ready configuration.
A third well-publicized attempt at overcoming the deficiencies of prior aircar projects is the very recent project of Ken Wernicke's of Sky Technology in Hurst, Texas. Wemicke's design sidesteps car-to-plane and plane-to-car transformations by using low-aspect-ratio wings that are wider than they are long. Elaborate winglets on the end of the broad wings boost aerodynamic efficiency and make the Aircar about as wide and as long as a bus, at 8.5 ft (2.6 m) in width and 22 ft (6.7 m) in length. Even then, Wernicke's own wind tunnel data, which is disclosed in U.S. Pat. No. 5,435,502, reveal that his design's maximum lift to drag ratio (L/D) is only 7.5 at lift coefficient of only 0.3, which is only a little more than 1/2 of the L/D of conventional private aircraft. The L/D got much worse, however, at higher lift coefficient that is required at take-off and landing speed, in which case, a lift coefficient of as much as 1.4 to 2.6 is required for take-off and landing at smaller municipal airports. At the lift co-efficient above 1.0, the L/D of the Aircar gets less than 2, whereas in a conventional aircraft at this lift co-efficient the L/D remains around 10. This means that Wernicke's Aircar will require much more power at the slow flight speed at take-off and landing, will not be able to achieve a reasonable service ceiling due to its tremendously high induced drag at higher wings lift coefficient, and that when the engine quits it will literally fall like a brick when turning or slowed down prior to landing. This certainly does not inspire pilot's confident in a single engine aircraft's ability to survive a power-off (or dead-stick) landing. There are other questions regarding Wernicke's design with respect to pitch and roll stability in an aircraft without a horizontal stabilizer and with such a short wing span, and questions regarding its ground handling in a tricycle configuration with such a high center of gravity off the ground and such tall winglets far aft of the center of gravity.
Among those less well publicized roadable aircraft designs, including at least 76 patented designs granted between 1918 and 1993, none has been able to simultaneously solve the large number of problems inherent in a typical roadable aircraft design such as excessive weight, aerodynamic inefficiency and poor stability in comparison to a typical light airplane, time and labor consuming conversion between ground and air modes, poor ground handling in comparison to a typical automobile, and excessive complexity that translates into increase in production and maintenance cost as well as unreliability.
The prior art also includes various patents of sub-class 244/46 disclosing fixed wing aircrafts with mechanism for wing rotation 90 degrees with respect to the fuselage. To my knowledge, none of those are roadable aircrafts. They are either supersonic fighter such as in U.S. Pat. No. 4,998,689 of Woodcock, U.S. Pat. No. 3,971,535 of Jones and U.S. Pat. No. 3,155,344 of Vogt. All these designs involve wing rotation during flight therefore utilizes heavy and complex turet mechanisms capable of withstanding the full stresses in flight that are not adaptable to the lighter roadable aircraft that does not need to rotate its wing while flying. Other wing rotation mechanisms in the prior art are designed for much larger commercial or military transport aircrafts that must rotate their wing only for compact storage purpose. Their mechanisms are also too complex, too expensive and rotate too slowly for use in a light personal aircraft that must quickly transform from roadable mode to aircraft mode within a few seconds while cruising in the highway above the minimum highway speed. For examples, Rumberger et al. of U.S. Pat. No. 5,337,974 discloses a wing rotation mechanism for storage of the V-22 tilt-rotor aircraft involving a large diameter unitary ring structure as the wing bearing. This large ring structure must be precisely shaped, which involved high cost and inherently give rise to lots of friction during wing rotation, therefore rapid wing rotation is difficult, not that this necessary in its role for the tilt-rotor aircraft. Furthermore, Rumberger's design does not provide for a mechanism of wing to fuselage sealing, thus requiring very high production tolerance of the rotating surfaces involved thus further increases cost, but in a defense related project, cost concern is perhaps not a high priority. Nor does Rumberger's design provide for vibration damping between the wing and the fuselage, perhaps causing more fatigue and wear on the metal parts involved.